This invention relates to a process and apparatus for the anerobic biological treatment of wastewater containing organic pollutants, and in particular to a process wherein the water is conducted through at least one reactor wherein the anaerobic microorganisms are incorporated at a carrier material.
Such anaerobic wastewater treatment methods have been known for a long time. The carrier material, usually of crushed rock, slag, or activated carbon, functions, on the one hand, to prevent the anaerobic microorganisms from being entrained with the treated wastewater effluent and, on the other hand, to provide, surface area for thorough contact in the reactor between the wastewater to be treated and the biomass. This process, however, has the disadvantage that the wastewater, in following the path of least resistance, "short circuits", resulting in only a portion of the surface area of the carrier material coming into contact with the wastewater. Furthermore, a gradual movement of the carrier particles, for improving mass transfer and conversion, is not readily possible due to the character of the material, and would in any event lead to extensive erosion of the carrier material proper. Moreover, especially when using reactors having a relatively high ratio of length to diameter, i.e. a reactor with only minor back mixing, there is the danger that with a high concentration of the organic substrate, the anaerobic bacteria will be inhibited in their growth or even destroyed. Conversely, if the loading of the carrier material with the substrate is kept sufficiently low so as to avoid damage to the biomass, there is still the danger, especially in case of a low laminar flow of the wastewater to be treated through the reactor, that the growth rate of the biomass on the carrier material will become so high that clogging of the reactor will occur.